I heard the Messenger of Allah ﷺ say, "When the buyer and seller disagree and there is no evidence between them, the word is that of the owner of the goods, or they call off the transaction."
أخبرنا محمد بن إدريس قال حدثنا عمر بن حفص بن غياث قال حدثنا أبي عن أبي عميس قال حدثني عبد الرحمن بن محمد بن الأشعث عن أبيه عن جده
سمعت رسول الله ﷺ يقول إذا اختلف البيعان وليس بينهما بينة فهو ما يقول رب السلعة أو يتركا
Hasan. It was narrated by Abu Dawud in Al-Buyu, chapter "When the two parties to a sale disagree and the item sold still exists," 3:511, from the hadith of Umar bin Hafs, transmitted through him, and it is also in Al-Kubra, no. 6244. Ibn Jarud graded it sahih, no. 625, as did Hakim, 2:45, and Dhahabi. Bayhaqi said, 5:332, "This is a hasan, connected chain." The hadith has corroborating narrations.